“Every time I fire a linguist, the performance of our speech recognition system goes up.”

Although its fame and iconic status are undisputed, the quip's context is unknown and its specific wording and dating are unclear. According to Daniel Jurafsky and James H. Martin, Jelinek himself recalled the quote as "Anytime a linguist leaves the group the recognition rate goes up" and dated it to December 1988 (Wayne, Pennsylvania), further noting that the quote did not appear in the published proceeding, whereas Roger K. Moore gave the wording as "Every time we fire a phonetician/linguist, the performance of our system goes up" and dated it to an IEEE Automatic Speech Recognition and Understanding workshop held in 1985.
Source: [Jurafsky, Daniel, James H. Martin, 2009, Speech and language processing: an introduction to natural language processing, computational linguistics, and speech recognition, 2nd, Prentice Hall series in artificial intelligence, Upper Saddle, New Jersey, Prentice Hall, 0-13-187321-0, 83]
Source: [Palmer, Martha, Tim Finin, 1990, Report on the Workshop on the Evaluation of Natural Language Processing Systems, Computational Linguistics, 16, 1, 171–185, http://www.cs.umbc.edu/~finin//papers/acl90.pdf]
Source: [Moore, Roger K., 2005, Results from a Survey of Attendees at ASRU 1997 and 2003, INTERSPEECH-2005, Lisbon, September 4-8, 2005, http://staffwww.dcs.shef.ac.uk/people/R.Moore/publications/Results%20from%20a%20Survey%20of%20Attendees%20at%20ASRU%201997%20and%202003.pdf]